Process for producing hollow cast article

ABSTRACT

A process for producing a hollow metal cast product having a desired interior contour is provided. The process comprises the steps of preparing a first lost model having an outer contour substantially corresponding to a desired interior contour of the finished product, depositing a metallic or ceramic material or a mixture thereof over the surface of said first lost model by spraying to form a layer defining a hollow core block, placing said hollow core block in a first mold, pouring or injecting a material for forming a second lost mold into said first mold to form a second lost model, coating a refractory material over said second lost model to form a second mold for casting, removing second lost mold to form a cavity, casting a molten metal or alloy into said cavity, and staving said second mold to take out a finished product.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a process for producing acast article having a hollow cavity, and more particularly to a processfor producing a hollow cast article having a desired interior contourdefined by a very smooth inner wall surface.

2. Related Art Statement

A core mold has conventionally used in the prior art casting process forproducing a hollow cast article having an interior cavity surrounded bya smooth inner wall surface, particularly when the interior cavity has acomplicated contour. In case where it is desired that the cast producthas an extremely smooth inner wall surface defining the interior cavity,a ceramic mold has been hitherto been used as the core mold. In general,such a core mold is prepared initially by molding a green core mold froma mixture of an aggregate, such as alumina or zirconia, and a binder,such as ethyl silicate, and then baking the green core mold. However, itis difficult to prepare a baked core mold of precise dimension, sincethe green material therefor tends to shrink or expand during the bakingstep to loose its dimensional stability. Other problems of theconventional ceramic core mold are that the quality thereof becomesoften irregular and that the production efficiency thereof is inferiorleading to high production cost.

OBJECT AND SUMMARY OF THE INVENTION

Accordingly, the principal object of this invention is to provide aprocess for producing a hollow metal cast product having an inner cavitysurrounded by a smooth wall surface at a high production efficiency andat high dimensional stabilty.

Another object of this invention is to provide a hollow metal castproduct without the use of a ceramic core mold which requirespreliminary baking step.

Other objects and advantages of this invention will become apparent fromthe following detailed description.

According to the present invention, there is provided a process forproducing a hollow metal cast product comprising the steps of preparinga first lost model having an outer contour substantially correspondingto a desired interior contour of the finished product, depositing amolten metal or alloy over the surface of said first lost model byspraying to form a metal layer defining a hollow core block, placingsaid hollow core block in a first mold, pouring or injecting a materialfor forming a second lost model into said first mold to form a secondlost model layer, coating a refractory material over said second lostmodel layer to form a second mold for casting, removing said second lostmodel to form a cavity, casting a molten metal or alloy into saidcavity, and staving said second mold to take out a finished product.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram showing the successive steps of an embodimentof the process of this invention;

FIG. 2 is a schematic illustration showing the steps of the process ofthis invention; and

FIG. 3 is a perspective view, with portions broken away, of a castproduct produced according to this invention.

DESCRIPTION OF THE INVENTION

The present invention will now be described in detail with reference topreferred embodiments thereof.

Referring to FIGS. 1 and 2, prepared at the first step (step 100) is afirst lost wax model 10 having an outer contour which is agreed with thedesired interior contour of the finished cast product. This first lostwax model 10 may be molded by any known methods, such as an injectionmolding process, and may be made of a plastic material which may bemelted by heating. Preferable examples of the material for the firstlost wax model include natural and synthetic waxes such as paraffin waxand water-soluble waxes, and moldable synthetic resins such aspolystyrene, urea resin and foamed polystyrene. The thus prepared firstlost wax model is carried by a proper support to be ready for the nextstep.

The next step (step 102, see FIG. 2(A)) is the step of depositing amolten metallic material or ceramic material over the surface of thefirst lost wax model by spraying to form a metallic or ceramic layer 12.The metallic material used in this step is not particularly limited, andvarious metals and alloys may be used singly or in combination.Alternatively, the layer 12 may be made of a mixture of one or moremetallic materials with one or more ceramic materials. When it isdesired to form the layer 12 by two or more metallic and/or ceramicmaterials, a mixture may be sprayed onto the surface of the first lostwax model 10, or one of them is first sprayed onto the surface of thefirst lost wax model followed by successive spraying of the remainingmetallic or ceramic materials to form a multi-plied coating.

The metallic or ceramic material may be deposited through a variety ofspray-depositing methods. For example, when the layer 12 is made of ametallic material, a selected metal wire is melted by electric spark andblown by compressed air to be sprayed onto the surface of the first lostwax model. Alternatively, a selected metal wire is melted by hightemperature flame and blown by compressed air to be sprayed onto thesurface of the first lost wax model. In a further modified method, ametal powder or a mixture of metal powders is melted by high temperatureflame and blown to be sprayed onto the surface of the first lost waxmodel. A so-called plasma metal spraying method may also be used in thisstep 102. It is desirous that either one of the molten metal spray gunor the first lost wax model is continuously moved to prevent a certainportion of the outer periphery of the lost wax model from being heatedexcessively by the applied molten metal to a temperature at which thelost wax model is melted.

This step 102 may also be carried out in an electric field to improvethe effective use of the sprayed metallic material. In such a method,the first lost wax model 10 is made of an electrically conductivematerial or the surface thereof is coated with a conductive material.The first lost wax model may be electrically conductive, for example, byusing a wax mixture containing a surfactant or emulsifier and wateruniformly dispersed in a commercially available wax. The surface of thefirst lost wax model may be electrically conductive, for example, bycoating a conductive material, such as a mixture of a surfactant andwater. Then, a molten metallic material is sprayed out of the nozzle ofa spray gun while a DC potential is applied between the gun and thesurface of the first lost wax model. Whereupon, the fine particles ormists of molten metallic material are charged with electricity of onepolarity and thus attracted by the first lost wax model 10 charged withelectricity of the other polarity, so that the ratio or part of theblown metallic material particles wastefully consumed without depositingon the surface of the model 10 can be decreased, or in other words, toincrease the ratio of the metallic material which has been effectivelyused to form the metallic coating or layer 12.

It is desirous that the molten metal spraying is implemented in an inertgas atmosphere when an easily oxidizable metal or alloy is used. Forexample, when a molten magnesium or titanium alloy is sprayed onto thesurface of the first lost wax model, the molten alloy is sprayed in aninert gas atmosphere, such as argon gas atmosphere. It is preferred thatthe same inert gas as that used to form the inert gas atmosphere is usedas the gas for blowing the molten metallic material from the spray gun.

Although a single metallic or ceramic material may be sprayed by asingle step or a mixture of metallic and/or ceramic materials may besprayed by a single step until a layer 12 having a desired thickness isformed, two or more different metallic or ceramic materials may bedeposited through plural separate spraying steps so that a multi-pliedcoating or layer 12 having a desired thickness is formed.

In the next step (step 104, see FIG. 2(B)), the first lost wax model 10applied with the coating or layer 12 is placed in position in a firstmold 14. Then, a material for forming a second lost wax model isinjected or otherwise filled in the cavity 16 defined between the layer12 and the inner periphery of the first mold 14 (step 106). At this step106, a second lost wax model 18 is molded so that it surrounds the outersurface of the spray-deposited layer 12. When the second lost wax model18 is molded by an injection molding process, it is desired that amaterial for the second lost wax model 18 has a melting point which islower than that of the wax material used for forming the first lost waxmodel 10 in order that the first lost wax model 10 is not melted duringthis step 106.

The composite model including the first and second lost wax models 10,18 and the spray-deposited layer 12 is then coated with a refractorymaterial, such as a ceramic material (step 108, see FIG. 2(C)). Indetail, the composite model is dipped in a slurry container and then thethus wetted composited model is applied with stacco particles. The cycleof dipping in the slurry container and applying with stacco particles isrepeated until the ceramic shell mold 20 has a desired thickness.

The next step (step 110) is a dewaxing step of heating to melt andremove the first and second lost wax models 10, 18. Then, the ceramicshell mold 20 is baked to obtain a baked ceramic shell mold (step 112,see FIG. 2(D)) in which the spray-deposited layer 12 is fixed inposition.

In the next step (step 114), a molten metal is cast in the cavity 16Acorresponding to the cavity 16 in the mold 14 and now defined by theinner periphery of the ceramic shell mold 20 and the spray-depositedlayer 12. After cooling to solidify the cast metal, the shell mold 20 isremoved (step 116).

Unnecessary portions are then cut away by machining to obtain a finishedproduct 22, as denoted by 120 in FIG. 1. Since the ends of thespray-deposited layer 12 are projecting from the end faces of thefinished product in the illustrated embodiment, the projecting endportions of the layer 12 are cut away by shearing or milling operation(see FIG. 2(E)).

It is preferable that the finished product is subjected to apost-heating treatment in order to increase the bonding force betweenthe spray-deposited layer 12 and the cast metal layer. In case where thespray-deposited layer 12 is a multi-plied layer made of plural metallicmaterials, the physical and chemical properties of the combined metallayer can be improved by alloying the different metals at the interfacethereof by this post-heating operation.

A portion of a product produced in accordance with the process of theinvention is shown in FIG. 3. The product shown in FIG. 3 is a casing 50for an electronic device having therein a spray-deposited layer 52serving as a wave guide tube. This casing 50 is produced, generallyfollowing to the sequential steps shown in FIG. 1, by initiallyspray-depositing an electrically conductive metal to form the layer 52having a generally rectangular and stepped section and then casting analuminium alloy over the layer 52 by a lost wax casting process. Thecasing 52 having a relatively complex shape and a portion made of adifferent material as that forming the remaining portion may be easilyproduced by the application of the process of this invention.

What is claimed is:
 1. A process for producing a hollow metal castproduct comprising the steps of preparing a first lost model having anouter contour substantially corresponding to a desired interior contourof the finished product, depositing a molten metal or alloy over thesurface of said first lost model by spraying to form a metal layerdefining a hollow core block, placing said hollow core block in a firstmold, pouring or injecting a material for forming a second lost modelinto said first mold to form a second lost model layer, coating arefractory material over said second lost model layer to form a secondmold for casting, removing said second lost model to form a cavity,casting a molten metal or alloy into said cavity, and staving saidsecond mold to take out a finished product.
 2. The process according toclaim 1, wherein two or more different metals or alloys are depositedconcurrently to form said metal layer defining said hollow core block.3. The process according to claim 1, wherein two or more differentmetals or alloys are deposited one after another to form a multi-layeredmetal layer defining said hollow core block.
 4. The process according toclaim 1, wherein said first lost model is electrically conductive, andwherein an electric potential is applied between said conductive firstlost model and a spray gun for electrodepositing said molten metal atthe step of depositing a molten metal or alloy to form said metal layerdefining said hollow core block.
 5. The process according to claim 1,wherein said first lost model is composed of a wax and said second lostmodel is composed of a different wax having a melting point lower thanthat of the wax forming said first lost model.
 6. The process accordingto claim 1, wherein said hollow core block has protruding ends or edgesfor ensuring precise positioning thereof in said first mold.
 7. Aprocess for producing a hollow metal cast product comprising the stepsof preparing a first lost model having an outer contour substantiallycorresponding to a desired interior contour of the finished product,depositing a molten ceramic material over the surface of said first lostmodel by spraying to form a ceramic layer defining a hollow core block,placing said hollow core block in a first mold, pouring or injecting amaterial for forming a second lost model into said first mold to form asecond lost model, coating a refractory material over said second lostmodel to form a second mold for casting, removing said second lost modelto form a cavity, casting a molten metal or alloy into said cavity, andstaving said second mold to take out a finished product.
 8. The processaccording to claim 7, wherein two or more different ceramic materialsare deposited concurrently to form said ceramic layer defining saidhollow core block.
 9. The process according to claim 7, wherein two ormore different ceramic materials are deposited one after another to forma multi-layered ceramic layer defining said hollow core block.
 10. Theprocess according to claim 7, wherein said first lost model iselectrically conductive, and wherein an electric potential is appliedbetween said conductive first lost model and a spray gun forelectrodepositing said molten ceramic material at the step of depositinga molten ceramic material to form said ceramic layer defining saidhollow core block.
 11. The process according to claim 7, wherein saidfirst lost model is composed of a wax and said second lost model iscomposed of a different wax having a melting point lower than that ofthe wax forming said first lost model.
 12. The process according toclaim 7, wherein said hollow core block has protruding ends or edges forensuring precise positioning thereof in said first mold.
 13. A processfor producing a hollow metal cast product comprising the steps ofpreparing a first lost model having an outer contour substantiallycorresponding to a desired interior contour of the finished product,depositing a metal and a ceramic material over the surface of said firstlost model by spraying to form a composite layer defining a hollow coreblock, placing said hollow core block in a first mold, pouring orinjecting a material for forming a second lost model into said firstmold to form a second lost model, coating a refractory material oversaid second lost model to form a second mold for casting, removing saidsecond lost model to form a cavity, casting a molten metal or alloy intosaid cavity, and staving said second mold to take out a finishedproduct.
 14. The process according to claim 13, wherein one or moremetal and one or more ceramic material are deposited concurrently toform said layer defining said hollow core block.
 15. The processaccording to claim 13, wherein one or more metal and one or more ceramicmaterial are deposited one after another to form a multi-layered layerdefining said hollow core block.
 16. The process according to claim 13,wherein said first lost model is electrically conductive, and wherein anelectric potential is applied between said conductive first lost modeland a spray gun for electrodeposition of said metal and said ceramicmaterial to form said composite layer defining said hollow core block.17. The process according to claim 13, wherein said first lost model iselectrically conductive, and wherein an electric potential is appliedbetween said conductive first lost model and a spray gun forelectrodeposition of either one of said metal or said ceramic materialto form said composite layer defining said hollow core block.
 18. Theprocess according to claim 13, wherein first lost model is composed of awax and said second lost model is composed of a different wax having amelting point lower than that of the wax forming said first lost model.19. The process according to claim 13, wherein said hollow core blockhas protruding ends or edges for ensuring precise positioning thereof insaid second mold.